Method for producing ethylbenzene

ABSTRACT

An ethylbenzene production system comprises a reactor vessel, a vapor phase ethylene feed stream, a benzene feed stream entering the reactor vessel, and a product stream containing ethylbenzene exiting the reactor vessel. The reactor vessel has an ethylation section and a benzene stripping section, whereby fluid communication via integrated vapor and liquid traffic is maintained between the ethylation section and stripping section. The vapor phase ethylene feed stream contains 3 to 50 mol % ethylene and at least 20 mol % methane entering the reactor vessel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.09/175,643, filed on Oct. 20, 1998, now U.S. Pat. No. 5,977,423, whichclaims priority of U.S. Provisional Application No. 60/089,968, filed onJun. 19, 1998, the disclosures of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention is directed to an improved process for producingethylbenzene.

PRIOR ART AND BACKGROUND OF THE INVENTION

Ethylbenzene, C₈H₁₀, is a key raw material in the production of styreneand is produced by the ethylation reaction of ethylene, C₂H₄, andbenzene C₆H₆ in a catalytic environment. Old ethylbenzene productionplants, typically built before 1980, used AlCl₃ or BF₃ as acidiccatalysts. The newer plants in general have been switching tozeolite-based acidic catalysts. The typical purity of the benzene feed,known as nitration grade benzene, is 99.9 wt %. The typical purity ofthe ethylene feed would exceed 99.9 mol %.

A significant source of crude benzene is pyrolysis gasoline (C₅ to C₉),which typically contains 55-75 wt % aromatics. Pyrolysis gasoline,produced in naphtha based or heavy liquid based olefin plants, contains35-55 wt % benzene. About 35% of world's benzene production capacityoriginates from pyrolysis gasoline. Typically, after pyrolysis gasolineis hydrotreated for saturation of olefins and di-olefins, the pyrolysisgasoline (free of olefins and sulfur compounds) is exported to batterylimits for aromatics extraction process. Pure benzene, 99.9 wt %, alongwith toluene and xylene, is a typical product of aromatic extraction.

Impure benzene, 94-98 wt %, which is a 75-83° C. atmospheric cut, can berecovered from hydrotreated pyrolysis gasoline by a simple fractionationprocess, as described in U.S. Pat. No. 5,880,320, the disclosure ofwhich is incorporated herein by reference.

Three types of ethylation reactor systems are used for producingethylbenzene, namely, vapor phase reactor systems, liquid phase reactorsystems, and mixed phase reactor systems. In vapor-phase reactorsystems, the ethylation reaction of benzene and ethylene is carried outat about 380-420° C. and a pressure of 9-15 kg/cm²-g. In most cases,these systems use ethylene feed in pure form as produced in conventionalolefin plants. Dilute ethylene streams, about 10-15 vol %, as producedin fluid catalytic cracking (FCC) in petroleum refining, are convertedto ethylbenzene using vapor phase reaction. One known facility wasdesigned by Raytheon Engineers & Constructors and is operated by ShellChemicals at UK. Similar facilities for FCC off-gases were built inChina by Sinopec.

Vapor phase reactor systems comprise multiple fixed beds of zeolitecatalyst. Ethylene exothermally reacts with benzene to formethylbenzene, although undesirable chain and side reactions also occur.About 15% of the ethylbenzene formed further reacts with ethylene toform di-ethylbenzene isomers (DEB), tri-ethylbenzene isomers (TEB) andheavier aromatic products. All these chain reaction products arecommonly referred as polyethylated benzenes (PEBs). In addition to theethylation reactions (at times referred to in the industry as alkylationreactions), the formation of xylene isomers as trace products occurs byside reactions. This xylene formation in vapor phase can yield anethylbenzene product with about 0.05-0.20 wt % of xylenes. The xylenesshow up as an impurity in the subsequent styrene product, and aregenerally considered undesirable.

Additionally, traces of propylene may enter the system with the ethylenefeed or are formed by catalytic cracking of non-aromatic impurities thatmay enter with the benzene feed. The presence of propylene results inthe formation of isopropyl benzene, commonly known as cumene, which isvery undesirable in the ethylbenzene at concentrations above 150 PPM.The cracking of non-aromatic impurities is accelerated by increasing theethylation reaction temperature, and thus substantial cracking ofnon-aromatic impurities to propylene occurs if the ethylation ortransalkylation reaction is at temperatures of above 300° C. and inpresence of acidic catalyst. This may result in an unacceptable level ofcumene in the ethylbenzene product.

In order to minimize the formation of PEBs, a stoichiometric excess ofbenzene, about 400-900% per pass, is applied, depending on processoptimization. The effluent from the ethylation reactor contains 70-85 wt% of unreacted benzene, 12-20 wt % of ethylbenzene product and about 3-4wt % of PEBs. The PEBs are converted back to ethylbenzene to avoid ayield loss.

The effluent of the ethylation reactor can undergo ethylbenzene productrecovery by several multiple fractionation stages. Benzene can berecovered in a benzene recovery column by stripping and can be recycledto the ethylation reactor. Ethylbenzene product can be recovered in anethylbenzene recovery column. DEB and TEB can be separated from heavieraromatics in a PEB column. The heavy aromatics can be diverted to thefuel oil system.

The DEB and TEB mixture proceeds to a transalkylation reactor systemwhere stoichiometric excess (250-300%) of benzene reacts with DEB andTEB in vapor phase at about 420-450° C. About 60-70% of the PEB isconverted to ethylbenzene per pass. The effluent product oftransalkylation reactor consists of ethylbenzene, un-reacted benzene andunconverted PEBs. This transalkylated stream undergoes stabilization forlight ends removal and is recycled to fractionation in the benzenecolumn. The ultimate conversion of DEB and TEB to ethylbenzene isessentially 100%.

The boiling point of the xylene isomer trace products is very close tothat of the ethylbenzene, and thus no practical separation is possible.The ethylbenzene product typically contains 500-2,000 PPM by weight ofxylene isomers, as well as 1000-2,000 PPM by weight of benzene.

In recent years the trend in industry has been to shift away from vaporphase reactors to liquid phase reactors. Liquid phase reactors operateabout 260-270° C., which is under the critical temperature of benzene,290° C. One advantage of the liquid phase reactor is the very lowformation of xylenes and oligomers. The rate of the ethylation reactionis lower compared with the vapor phase, but the lower design temperatureof the liquid phase reaction usually economically compensates for thenegatives associated with the higher catalyst volume. The stoichiometricexcess of benzene in liquid phase systems is 150-400%, compared with400-800% in vapor phase. However, due to the kinetics of the lowerethylation temperatures, resulting from the liquid phase catalyst, therate of the chain reactions forming PEBs is considerably lower; namely,about 5-8% of the ethylbenzene is converted to PEBs in liquid phasereactions versus the 15-20% converted in vapor phase reactions.Transalkylation reaction, where polyethylated benzene reacts withbenzene to form ethylbenzene, can occur in a liquid phase or vapor phasesystem. The liquid phase reaction temperature would be 230-270° C. Thefractionation sequences and product recovery methods for liquid phasereaction systems are similar to those used in connection with vaporphase reactor systems.

In recent years, technology has been developed for the production ofethylbenzene from dilute ethylene streams by a mixed phase reactor. Thedemonstrated dilute ethylene stream sources are from petroleumrefineries, fluid catalytic cracking operation (FCC). ABB Lummus Globaland CDTech have developed a mixed phase process. Aside from ethylationreactors, the sequence of the ethylbenzene product recovery andtransalkylation is similar to the conventional liquid phase reactorsystems.

A potentially alternate source of dilute ethylene is described in U.S.Pat. No. 5,880,320. The dilute ethylene stream is extracted from thedemethanizer section of the ethylene plant at about 22-30 kg/cm²-g.Dilute gas from ethylene plants may contain 7-25 mol % ethylene, and thebulk of the balance is methane and hydrogen. The propylene content iscontrolled at the ethylene source to remain below 20 PPM by volume.

The use of a liquid phase reaction system for dilute ethylene streams isnot possible. Due to the high methane and hydrogen content in theethylene stream, the bubble point temperature of the combined mixture ofdilute ethylene and benzene is very low, lower than the activitytemperature of the ethylation catalyst, and actually below the freezingpoint of benzene.

The reaction temperature of the mixed phase ethylation reactor is underthe dew point of the dilute ethylene benzene mixture, but well above thebubble point. The diluents of the ethylene feed comprise hydrogen,methane and small amounts of ethane, and CO remains essentially in thevapor phase. The benzene in the reactor is split between vapor phase andliquid phase, and the ethylbenzene and PEB reaction products remainessentially in liquid phase.

In the alkylation and transalkylation of aromatic hydrocarbons, zeolitecatalysts have been shown to be an adequate substitute for acidiccatalysts, such as aluminum chloride (AlCl₃), boron trifluoride (BF₃),liquid and solid phosphoric acid, sulfuric acid and the like. Forexample, U.S. Pat. No. 2,904,607 shows alkylation of aromatics in thepresence of a crystalline aluminosilicate having a uniform pore openingof 6 to 15 angstroms.

U.S. Pat. No. 3,641,177 describes an alkylation process wherein thecatalyst has undergone a series of ammonium exchange, calcination andsteam treatments. This catalyst would currently be described as an“ultrastable” or “steam-stabilized” zeolite Y catalyst.

U.S. Pat. Nos. 3,751,504 and 3,751,506 show transalkylation andalkylation over ZSM-5 type catalysts. Use of other medium-pore tolarge-pore zeolites are taught in U.S. Pat. No. 4,016,245 (ZSM-35), U.S.Pat. No. 4,046,859 (ZSM-21), U.S. Pat. No. 4,070,407 (ZSM-35 andZSM-38), U.S. Pat. No. 4,076,842 (ZSM-23) U.S. Pat. No. 4,575,605(ZSM-23), U.S. Pat. No. 4,291,185 (ZSM-12), U.S. Pat. No. 4,387,259(ZSM-12), and U.S. Pat. No. 4,393,262 (ZSM-12) and European PatentApplication Nos. 7,126 (zeolite omega) and 30,084 (ZSM-4, zeolite beta,ZSM-20, zeolite L).

Liquid phase alkylation is specifically taught using zeolite beta inU.S. Pat. No. 4,891,458 and European Patent Application Nos. 0432814 and0629549. Novel dealuminized mordenites are described for these types ofreactions in U.S. Pat. Nos. 5,015,797 and 4,891,448.

More recently it has been disclosed that MCM-22 and its structuralanalogues have utility in these alkylation/transalkylation reactions.U.S. Pat. No. 4,992,606 (MCM-22), U.S. Pat. No. 5,258,565 (MCM-36), U.S.Pat. No. 5,371,310 (MCM-49), U.S. Pat. No. 5,453,554 (MCM-56), and U.S.Pat. No. 5,149,894 (SSZ-25). Additionally Mg APSO-31 is described as anattractive catalyst for cumene manufacture in U.S. Pat. No. 5,434,326.

U.S. Pat. No. 5,176,883 describes an integrated ethylation fractionationin general without diluants for the ethylene feed. U.S. Pat. No.5,043,506 describes the addition of n-C₅, n-C₆, and i-C₆ as a means forfractionation control in alkylation systems.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is directed to an ethylbenzeneproduction system comprising a reactor vessel, a vapor phase ethylenefeed stream and a benzene feed stream entering the reactor vessel, and aproduct stream containing ethylbenzene exiting the reactor vessel. Thereactor vessel has an ethylation section and a benzene strippingsection, whereby integrated vapor and liquid traffic is maintainedbetween the ethylation section and stripping section. Preferably thereactor vessel is a single unit, but can alternatively comprise aplurality of integrated units, so long as integrated vapor and liquidtraffic is maintained between the integrated units.

Dilute ethylene streams at a typical concentration of 7-25 mol % andless than 20 PPM of propylene will react with benzene at temperatures of155-195° C. and pressures of 22-30 kg/cm2-g to form ethylbenzene andsmall amount of PEBs. The benzene stripper generates an internal benzenetraffic in the ethylation section of about 300-400% stoichiometricexcess, but additional vapor traffic is generated by the heat ofreaction. The external stoichiometric excess of benzene is on the orderof 3-15% depending on purge rate, purge recovery, benzene losses to ventgas and formation of heavy aromatic product. The stripper's bottomproduct is essentially free of benzene and suitable for ethylbenzenefractionation.

Preferably the reactor vessel further comprises a rectifying section anda transalkylation section. Alternatively, the system can comprises atransalkylation section outside of the reactor vessel.

In a particularly preferred embodiment, the invention is directed to anethylbenzene production system comprising a reactor vessel, a vaporphase dilute ethylene feed stream and a benzene feed stream entering thereactor vessel, and a product stream containing ethylbenzene exiting thereactor vessel. The reactor vessel has an ethylation section and abenzene stripping section, whereby integrated vapor and liquid trafficis maintained between the ethylation section and stripping section. Thevapor phase dilute ethylene feed stream comprises ethylene in aconcentration of from about 3 to 50 mol % based on the totalconcentration of the ethylene feed stream. The benzene feed streamcomprises benzene and at least one non-aromatic compound, wherein theconcentration of benzene in the benzene feed stream is from about 75% toabout 100% by weight, based on the total weight of benzene andnon-aromatic compounds.

The methods of the invention are particularly useful for the utilizationof impure benzene, typically 94-98 wt %, with a balance of cyclohexaneand other non-aromatics. The source of this impure benzene would bepyrolysis gasoline, after hydrogenation and fractionation. Because thetemperatures of the ethylation and transalkylation reactions are below300° C., no significant cracking of non-aromatic occurs. Production ofxylene is very minimal if any.

Conventional zeolitic and nonzeolitic catalysts, with formulations inthe public domain, can be used. These catalysts have been traditionallyused for cumene manufacturing in a temperature range of 150-180° C. Inthe cumene reaction, propylene reacts with benzene to form isopropylbenzene; however, impurities of ethylene are also known to react withbenzene to form ethylbenzene. The non-aromatic impurities are allowed tobuild in the ethylation loop, prior to purging to a purge ethylationreactor. The economics of the assumed purge reactor would largely dependon the concentration of non-aromatic impurities in the benzene feed.

In another embodiment, the invention is directed to a method forenhancing the recovery of benzene from an impure benzene feed.Cyclohexane is included in the impure benzene feed. The temperature ofthe impure benzene feed is then reduced below the freezing point ofbenzene. Preferably the temperature of the impure benzene feed isreduced to a temperature ranging from about −6° C. to about 4° C., morepreferably from about −5° C. to about 0° C. Preferably the weight ratioof non-aromatics to benzene in the impure benzene feed ranges from about0.25 to about 0.7.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of the invention where thetransalkylation catalyst beds are an integrated section of the overallethylation reactor vessel.

FIG. 2 illustrates an alternative embodiment of the invention where thetransalkylation reactor is a liquid phase reactor and separated from themain reactor vessel.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of an ethylbenzene production system according to theinvention is depicted in FIG. 1. The ethylbenzene production systemcomprises a reactor vessel having several sections, namely an ethylationsection, 10B, a transalkylation section, 10C, a rectifying section, 10A,and a benzene stripping section 10D. The reactor vessel, althoughdepicted as a single vessel in FIG. 1, can be in the form of severalintegrated vessels, so long as the integrated vapor and liquid trafficis maintained between the ethylation and the stripping section.

The ethylation section, a fixed bed catalytic ethylation section, wherevapor phase ethylene and mixed phase benzene feed streams react to formethylbenzene and PEB, is an isothermal reactor. Because of the diluenteffect of the methane and hydrogen in the ethylene feed, the ethylationreaction is carried out at a temperature that is at least 10° C. lowerthan the normal boiling temperature of benzene at a given ethylationpressure. The invention is not intentionally directed to the use ofcatalytic distillation in the reactor. Cocurrent, mixed current andcounter current flows would be formed, however, the thermodynamic effecton ethylene conversion by simultaneous separation of ethylbenzeneproduct is insignificant.

The heat of reaction and reboiler heat input to the system are recoveredas 3-8 kg/cm²-g steam, to be generated in the tubes when the catalyst isplaced in the shell. However, when the catalyst is placed in the tubes,the steam is generated in the shell. Additional steam at 1.5-2.0kg/cm2-g would be generated at the overhead condenser. The diluteethylene stream (containing methane and hydrogen) is introduced at thebottom of the catalytic ethylation section. The catalyst formulation isavailable at the public domain from cumene manufacturing technology.AlCl₃ catalysts, which are known to be active for ethylation reactionsat about 150° C., could also be considered as a viable option for thissystem. Hydrogen, methane, vapor phase benzene and cyclohexane pass tothe rectifying section, and ethylbenzene, PEB products, liquid phasebenzene and heavy aromatics pass to the transalkylation section.

Fixed beds of catalyst will serve as transalkylator using a vapor liquidmixture of benzene and impurities such as cyclohexane, however nodiluents of the ethylene feed the ethylbenzene and PEB will beessentially in liquid phase. The catalyst formulation for thetransalkylation can be identical to the one used for the ethylationsection. The heat effect of this reaction is nearly zero, and theoperating temperature range would be 220-250° C. depending on thepressure. The stoichiometric excess of benzene in the transalkylationsection is over 1000%, thus over 50 percent conversion of PEB toethylbenzene per pass occurs for the end of run.

The remaining PEBs (after transalkylation), along with the ethylbenzene,benzene, and heavy aromatics proceed to the benzene stripping section.The stripping section is at the bottom of the reaction vessel and is thesection where benzene stripping occurs. About 25 actual trays (15theoretical) or equivalent packing can be used. Stripping duty isprovided by a fired heater (or hot oil) providing thermal duty at about295-325° C., depending on the pressure. The unreacted benzene along withcyclohexane is driven to the catalytic section, creating a localizedexcess of benzene, which improves reaction equilibrium to minimize PEBformation. The stripping heat input also increases the ethylationreaction temperature, thus improving the ethylation rate of reaction andminimizing the amount of catalyst required.

The upper section of the reactor vessel acts as a rectifier where refluxof benzene washes down the ethylbenzene vapors for full productrecovery. Vent gas, depleted of ethylene, proceeds to residual benzenerecovery by refrigeration.

In a preferred embodiment, a purge reactor similar to the one of themain reactor vessel described above, but without transalkylationsection, could be included in the system. A purge stream from theethylation loop with 60 to 85 wt % benzene (73% in the demonstratedcase) reacts in a mixed phase with dilute ethylene. Because of the lowbenzene to ethylene ratio, the conversion of ethylbenzene to PEBs mayreach 50% or more. The bottom of the stripping section consists ofethylbenzene 35-65 wt % and the balance is PEBs along with traces ofbenzene. This stream is routed to the feed of the ethylbenzene column asshown in FIG. 1.

The off gas from the purge reactor is chilled for benzene andcyclohexane condensation. The off-gas, rich in unconverted ethylene,proceeds to the ethylene feed stream of the main ethylation reactor. Theresidual, non-converted liquid resulting from the ethylation of thepurge contains approximately 15-20 wt % benzene and the balancenon-aromatics, principally cyclohexane. This liquid is disposed to thepyrolysis gasoline export, or to a crude cyclohexane facility.

In an alternative embodiment, as shown in FIG. 2, the transalkylationsection is contained outside of the reaction vessel. This alternativedesign can be used if there is a concern of catalyst plugging anddeactivation by heavy aromatics, or if the reaction is being run at apressure below 20 kg/cm²g. The resulting operating temperature of below220° C. would deactivate the catalyst.

When an impure benzene feed is used (for example, a feed originatingfrom pyrolysis gasoline fractionation) the cyclohexane concentrationbuilds in the upper rectifying section. The freezing points of purebenzene and cyclohexane are +5.5° C. and +6° C., respectively. Theeutectic effect of cyclohexane buildup results in depression of thefreezing temperature of the mixture to approximately −17° C. to −10° C.(depending on the ratio of benzene to cyclohexane). Thus, the benzenemixture from the rectifying section can be cooled to a temperature of−5° C. or lower. The lower temperature permits a greater amount ofbenzene recovery from the vent gas. Thus benzene recovery byrefrigeration of the vent gas is a feasible approach, and the moreconventional vent gas scrubber using PEB liquid can be avoided. For purebenzene feed, a conventional vent scrubber is required, unlesscyclohexane is added to the overhead.

In U.S. patent application Ser. No. 08/957,252, the usage of impurebenzene is proposed in conjunction with hydrotreating and fractionationof pyrolysis gasoline in an adjacent olefin plant. Typically, thisimpure benzene resulting from pyrolysis gasoline includes about 2-6 wt %cyclohexane, depending on naphtha feed analysis and cracking severity inthe olefin plant. The non-aromatic impurities also include traces ofother C₆ and C₇'s. These impurities would be allowed to build to aweight ratio of 0.3-0.70 to the benzene in the reflux drum. The eutecticeffect of the impurities will allow the chilling the vent gas to −2° C.to −10° C., becoming an economical way to recover residual benzene. Somenon-aromatic impurities will escape with the vent gas, and most of itwould be purged as liquid. This methodology is described in U.S. patentapplication Ser. No. 08/957,252.

EXAMPLE

For illustration and consistency purposes, an ethylbenzene productionsystem for 380,000 tonne per year of ethylbenzene is described. Thestreams and apparatus designations are depicted in FIG. 1. The assumedproduction rate is based on 345 operating days per year. The diluteethylene feed (stream 1) to the facility is originated from a naphthabased olefin plant. Stream No. 1, at a pressure of 25 kg/cm²-g and atemperature of 30° C., has the following

Component kg-mol/hr Mol % Hydrogen 1,460 31.1 CO 21.0 0.44 Methane2748.0 58.6 Ethylene 448.0 9.6 Ethane 9.0 0.2 Propylene 0.02 5 PPMAcetylene 0.02 5 PPM Total 4686

Stream No. 2 contains impure benzene from a pyrolysis gasoline source.More specifically, Stream No. 2 comprises:

Component kg/hr kg-mol/hr wt % Benzene 38,200 490   96.0  Cyclohexane 1,400 16.6 3.5 Dimethyl pentanes   160  1.6 0.4 N-heptane and C₆/C₇Trace Trace Trace Toluene Trace Trace Trace Water Trace Trace 10 PPMSulfur Compounds Trace Trace 0.5 PPM (as sulfur) Total 39,760 508  

At the end of the run, there is a total ethylene utilization 98% and0.8% ethylene losses to heavy aromatics. Thus, 97.2% of the ethylene isconverted to ethylbenzene, and the balance is routed to gaseous andliquid fuels. Impurities build up in the liquid of the reflux drum 60 is27 wt %. The system does not contain a purge reactor. Ethylene entersthe bottom of the ethylation catalyst bed and reacts with benzene inliquid phase at 180° C. The heat of reaction, 12 MM Kcal/hr, about 975Kcal per kg of ethylene is mostly recovered by generating steam stream16 and vaporizing benzene. The benzene is recondensed at the overheadand the vent gas chilling system 50. About 5.0 % of the ethylbenzeneformed in the ethylation catalyst beds further reacts with ethylene.About 3.8% of the ethylbenzene ends as DEB, 1.0% as TEB, and thebalance, 0.2%, as heavier aromatics. The overhead of the ethylationcatalyst beds contains hydrogen, methane, benzene and small amounts ofethylbenzene and unconverted ethylene. The overhead gas from theethylation beds proceeds to the rectifying section 10A, about 5 to 7trays, where ethylbenzene is recondensed. Reactor vessel overhead gasstream 3 proceeds to condenser/steam generator 20, and steam at 2.0kg/cm²-g is generated. The gas is further cooled in heat exchange 30 toabout 65° C. by preheating tempered water from 50° C. about 80° C. Thegas is further cooled to 35° C. in heat exchanger 40 with 30° C. coolingwater. The vent gas at 35° C. is chilled at heat exchanger 50 to −5° C.,by using +12° and −8° C. refrigeration, for example, from the nearbyolefin plant. Liquid and vent gas products are separated in the refluxdrum 60 and reheated to 30° C. by cold recovery at heat exchanger 50.Vent gas, stream 13, at 22 kg/cm²-g and 30° C. proceeds to PSA hydrogenrecovery (not shown) or to a fuel gas system at the followingcomposition:

k-mol/hr Mol % Hydrogen 1,460 34.4  Methane 2,748 64.7  Ethane    9 0.2CO   21 0.5 Ethylene    9 0.2 Benzene    4 0.1 Cyclohexane     1.2 —Ethylbenzene Trace — PEB Trace — Total 4,252 100   

A purge, stream 4, of 5,300kg/hr of liquid from the reflux stream 17drum containing 73 wt % benzene is drawn from the reflux line at 30° C.By applying the optional purge reactor (not shown) the overall yield ofethylbenzene from benzene increases from 88% to 97%. The benzene yieldlosses will show as pyrolysis gasoline if no purge reactor is applied.

Liquid bottom product from the ethylation section 10-B, stream 12,contains benzene; cyclohexane ethylbenzene and PEB descend to thetransalkylation section 10-C along with recycle DEB and TEB. About 80%of the PEB is reconverted to ethylbenzene at the start of the run and50% at the end of the run. The material balance is based on end of runand transalkylation at 235° C.

Transalkylated product line, internal stream 6, proceeds to the benzenestripping section 10-D. Reboiler 80 provides the stripping duty of about16 MM Kcal/hr. Bottom product, stream 7, results from benzene strippingand has the following composition:

kg/hr kg-mol/hr wt % Ethylbenzene 46,100 435 87.0 DEB  5,200 39 9.8 TEB 1,400 8.5 2.6 Heavy   130 0.6 0.25 Benzene    70 1.0 0.13 Cyclohexane   10 0.2 0.02 Total 52,910

The bottom stripped product, stream 7, at 310° C., proceeds to theethylbenzene column 90. The overhead from the ethylbenzene column,stream 8, is ethylbenzene product with 1,500 PPM of benzene and 250 PPMof cyclohexane.

The bottom product from the ethylbenzene column stream 9 contains:

Ethylbenzene 200 kg/hr DEB 5,200 kg/hr TEB 1,400 kg/hr Heavy 130 kg/hr

This mixture, stream 9, proceeds to PEB column 100, where heavyaromatics, stream 11, are separated as bottom product. DEB and TEBoverhead, stream 12, recycle to the transalkylation section 10-C stream14, by combining with benzene feed, stream 2.

In the conservative design, FIG. 2, the conversion in the transalkylatorwill be 60% at liquid phase reactor at about 270° C. About 3,500 kg/hrof DEB and TEB would react with about 10,000 kg/hr of pure benzene feedfrom stream 15. The material balance at FIG. 2 is somewhat differentthan FIG. 1 and not shown.

What is claimed is:
 1. A method for producing ethylbenzene comprising:operating an isothermal ethylation section of a reactor vessel in asteady state mode, the isothermal ethylation section comprisingcatalytic media, the reactor vessel further comprising a benzenestripping section, where the stoichiometric excess, unreacted benzene isthermally stripped from the products, whereby integrated vapor andliquid traffic is maintained between the ethylation section and thebenzene stripping section; providing a vapor phase dilute ethylene feedstream entering the reactor vessel comprising hydrogen, methane, andethylene in a concentration of from about 3 to 50 mol % based on thetotal concentration of the ethylene feed stream; providing a benzenefeed stream entering the reactor vessel comprising benzene and at leastone non-aromatic compound wherein the concentration of benzene in thebenzene feed stream is from about 75% to about 100% by weight, based onthe total weight of benzene and non-aromatic compounds, and wherein theamount of benzene in the ethylation section results in stoichiometricexcess of benzene relative to ethylene; and reacting the ethylene withthe benzene to produce a product stream containing ethylbenzene and anoverhead gas comprising hydrogen, methane, unreacted ethylene,ethylbenzene and benzene exiting the ethylation section of the reactorvessel, wherein the ethylation reaction occurs at a temperature at least10° C. below the boiling point of benzene at the pressure at which thereaction is maintained; wherein the isothermal ethylation sectioncomprises a tubular structure and maintains a substantially constantreaction temperature in the catalytic media during the reaction ofethylene with benzene by simultaneous removal of heat from the catalyticreaction media via heat transfer across the surface of the tubularstructure.
 2. A method according to claim 1, wherein the concentrationof benzene in the benzene feed stream is from about 92% to about 100% byweight, based on the total weight of benzene and non-aromatic compounds.3. A method as claimed in claim 1 wherein the stoichiometric excess ofbenzene in the benzene feed stream to ethylene in the ethylene feedstream is less than 50%.
 4. A method as claimed in claim 1 wherein thestoichiometric excess of benzene in the benzene feed stream to ethylenein the ethylene feed stream is less than 15%.
 5. A method as claimed inclaim 1 wherein the stoichiometric excess of benzene in the benzene feedstream to ethylene in the ethylene feed stream is less than 5%.
 6. Amethod according to claim 1, further comprising providing a purgereactor and feeding an impure benzene mixture produced as a residualproduct in the ethylation section to the purge reactor, wherein theimpure benzene mixture comprises a higher concentration of the at leastone aromatic compound than the benzene feed stream to the reactorvessel, thereby producing a second residual product having a benzeneconcentration of below 30% by weight based on the total weight ofbenzene and non-aromatics present in the product.
 7. A method as claimedin claim 1, wherein the temperature of the ethylation section rangesfrom about 130° C. to about 220° C.
 8. A method as claimed in claim 1,wherein the temperature of the ethylation reaction ranges from about155° C. to about 195° C.
 9. A method as claimed in claim 1, wherein theoperating pressure inside the ethylation section ranges from about 7 toabout 33 kg/cm2-g.
 10. A method as claimed in claim 1, wherein theoperating pressure inside the ethylation section ranges from about 20 toabout 26 kg/cm2-g.
 11. A method as claimed in claim 1, wherein in theethylation section, steam is generated in steam tubes.
 12. A method asclaimed in claim 1, wherein the method produces an ethylbenzene productcontaining less than 150 PPM by weight of cumene.
 13. A method accordingto claim 1, wherein the ethylene feed stream comprises 3 to 50 mol %ethylene and at least 20 mol % methane.
 14. A method according to claim1, wherein the catalytic media is contained within the tubularstructure, whereby heat is transferred through the surface of thetubular structure, thereby generating steam outside the tubularstructure.
 15. A method according to claim 1, wherein the catalyticmedia is contained outside the tubular structure, whereby heat istransferred through the surface of the tubular structure, therebygenerating steam inside the tubular structure.
 16. A method according toclaim 1, wherein the benzene in the ethylation section of the reactorvessel is in a mixed vapor/liquid phase.
 17. A method according to claim1, wherein the overhead gas proceeds to a rectifying section of thereactor vessel, ethylbenzene is recovered by reflux wash with benzene,and residual vent gas comprising hydrogen, methane, unreacted ethyleneand benzene proceeds to benzene recovery by condensation.
 18. A methodfor producing ethylbenzene comprising: operating an ethylation sectionof a reactor vessel in a steady state mode, wherein the reactor vesselcomprises a mixed phase transalkylation section and a benzene strippingsection, where the stoichiometric excess, unreacted benzene is thermallystripped from the ethylation products, whereby fluid communication viaintegrated vapor and liquid traffic is maintained between the ethylationsection and the transalkylation section and between the transalkylationsection and the benzene stripping section; providing a vapor phaseethylene feed stream containing ethylene entering the reactor vessel;providing a benzene feed stream containing benzene entering the reactorvessel, wherein the amount of benzene in the ethylation section resultsin stoichiometric excess of benzene relative to ethylene; and reactingthe ethylene with the benzene to produce a product stream containingethylbenzene and an overhead gas comprising hydrogen, methane, unreactedethylene, ethylbenzene and benzene exiting the ethylation section of thereactor vessel, wherein the reaction occurs at a temperature at least10° C. below the boiling temperature of benzene at the pressure at whichthe reaction is maintained.
 19. A method according to claim 18, whereinthe benzene in the ethylation section of the reactor vessel is in amixed vapor/liquid phase.
 20. A method according to claim 18, whereinthe overhead gas proceeds to a rectifying section of the reactor vessel,ethylbenzene is recovered by reflux wash with benzene, and residual ventgas comprising hydrogen, methane, unreacted ethylene and benzeneproceeds to benzene recovery by condensation.
 21. A method according toclaim 20, further comprising introducing a source of at least onenon-aromatic C₅ to C₇hydrocarbon to the benzene feed stream orfractionation system to depress the solid formation temperature of theoverhead gas to below 5.5° C.
 22. A method according to claim 20,further comprising introducing a source of at least one non-aromatic C₅to C₇hydrocarbon to the benzene feed stream or fractionation system todepress the solid formation temperature of the vent gas to below about5.5° C.
 23. A method according to claim 18, wherein the ethylationsection is an isothermal ethylation section comprising catalytic media,wherein the isothermal section comprises a tubular structure andmaintains a substantially constant reaction temperature in the catalyticmedia during the reaction of ethylene with benzene by simultaneousremoval of heat from the catalytic reaction media via heat transferacross the surface of the tubular structure.
 24. A method according toclaim 23, wherein the catalytic media is contained within the tubularstructure, whereby heat is transferred through the surface of thetubular structure, thereby generating steam outside the tubularstructure.
 25. A method according to claim 23, wherein the catalyticmedia is contained outside the tubular structure, whereby heat istransferred through the surface of the tubular structure, therebygenerating steam inside the tubular structure.
 26. A method according toclaim 18, further comprising providing a purge reactor and feeding animpure benzene mixture produced as a residual product in the ethylationsection to the purge reactor, wherein the impure benzene mixturecomprises a higher concentration of the at least one aromatic compoundthan the benzene feed stream to the reactor vessel, thereby producing asecond residual product having a benzene concentration of below 30% byweight based on the total weight of benzene and non-aromatics present inthe product.